1. Field of the Invention
The invention relates to a method of processing a material with a first and a second surface by means of a laser beam which for instance by means of a multilens objective is focused in a number of focal points, where said focal points are approximately positioned on a common axis forming an angle with the first surface and are spaced apart.
2. Discussion of the Background
German Auslegeschrift No. 2,713,904 discloses a way of processing an article by means of a laser beam, said laser beam being focused in two focal points by means of a multilens objective. This processing method is used for drilling holes, whereby one focused bundle of rays is used for a melting of the surface of the article and the second bundle of rays presents a focal point positioned below the focal point of the first bundle of rays and is used for preheating the area surrounding the location of the article to be melted so as subsequently to be removed by way of evaporation. Such a processing method avoids to a certain degree formation of burrs at the edge of the hole. The lower focal point is, however, not utilized.
A growing demand has applied within the material processing industry employing lasers for a possibility of cutting in thick plates, such as steel plates of a thickness of 15 mm or more. As the cutting capacity of the laser beam is best on or adjacent the surface it is focused on, problems apply to transferring the effect to portions of the plate positioned below said surface. Moreover, the second surface of the material is encumbered with problems of an increased amount of adhering slags and a poor cutting quality, which inter alia results in a poor separation of the cut parts and may necessitate a finishing processing.